Air Carrier Captain reported receiving a warning of smoke in the cargo compartment and returned to departure airport. The Captain reported the QRH does not adequately explain the procedure to resolve this warning.

Narrative

We took off on Runway XXR on the ZZZZZ departure. Climbing through 29000 ft.; we received AFT COMPT LOOP FAULT. I leveled off at 30000 ft. and we ran the QRH checklist. We then received the CARGO COMPT SMOKE ECAM message and a Master Caution. I took over ATC comm 1 radio and [advised ATC] and requested return to ZZZ. The FO (First Officer) continued the checklist; changed the destination and set us up for a return to Runway XYR at ZZZ. We had an uneventful landing and the fire department used thermal cameras to check for heat signature in the AFT compartment. No indications were seen and we taxied back to the ramp.This is an edited version of my first [report] from this event. I was PF (Pilot Flying). We took off on [Runway] XXR on the ZZZZZ departure. Climbing through 29000 ft.;we had a AFT COMPT LOOP FAULT ECAM message with a Cargo Loop Fault procedure. My FO (First Officer) opened the QRH to the Cargo Loop Fault checklist. After further reflection on our actions during the event and referencing the Systems manual and QRH again; I realized the Cargo Loop Fault checklist does not fully explain how to do a Loop Test. The checklist states; 'Loop Test - Perform' but does not go into detail on HOW to perform a loop test. The systems manual does; and on step X. Loop Test Pushbutton it states - 'Pressed and held IN'. My FO did not press and hold in the Loop Test button; he only pressed and released it. The next sentence in the QRH Cargo Loop Fault checklist states; 'If SMOKE light does not illuminate for affected compartment (smoke condition exists):' My FO and I looked at each other and said; 'We must have smoke.' We then continued the checklist by RE-SELECTING LOOP A (which had faulted) and turned OFF the OTHER LOOP. Almost immediately we received the CARGO COMPT SMOKE ECAM Master Warning and chime as the checklist states; Procedure: CARGO COMPT SMOKE. I took over ATC communications 1 radio and [requested priority handling]; requested return to ZZZ as the FO continued the checklist; changed the destination and set us up for a return to XYR back at ZZZ. Uneventful landing and the fire department used thermal cameras to check for heat signature in the AFT compartment. No indications were seen and we taxied back to the ramp. If you look at the [Aircraft] System manual; you can see the photo of the Lower Cargo Smoke Detection system and see that by re-selecting a faulted LOOP A; and turning OFF the good LOOP B; you will receive a SMOKE detection; which is what we had. In addition; if you turn the page in the QRH you will see 'Additional Information' which uses the example of an Illuminated LOOP A fault. This information is very important and a reference to it should be included on page XXX of the QRH. I would recommend a change to the QRH CARGO LOOP FAULT checklist to edit the 'LOOP TEST - PERFORM' to closely match the Systems manual and should read; 'LOOP TEST - PRESS AND HOLD IN'. ALL lights on the Cargo Compartment Smoke Detection panel should illuminate which will confirm a faulty loop (see second boldfaced sentence). If the SMOKE light does NOT illuminate for affected compartment; smoke condition exists. If you flip the two boldface sentences; the checklist will make more sense after you 'perform a loop test' by holding the button IN. Since our FO's do not perform a Main Deck or Cargo compartment LOOP test during their preflight; they may not understand you must hold the button in to do the loop test.