Found the solution by myself.
Here are the steps:
1) Remove all the knobs from the front panel.
2) Unscrew all the bolts securing the pots.
3) Carefully pull out the front panel (take care do not drop the bushing surrounding each push button)
4) Unscrew two screws holding the three FAST/VAR PERSIST/BISTABLE pushbuttons. It's a little pcb, A17 storage mode switch board. Pull the harmonica connector that connect it to the storage board: connector P1400 (A17)<->P1404 (A14). Remove the assembly.
Now the R1472A/B pot can be carefully extracted from its recess for cleaning. Eventually pull out P1475 that connects the dual pot to the storage board for greater ease.