The indicator on the Alba tap can be taken off using your finger nail. Please note that the picture examples shown here are of the Carron Phoenix Opus Tap but the principle is the same. There are further images also in the blog link below.
Then use a flat headed screwdriver to remove the brass screw as in the example shown here in the pictures.
This will release the handle from the tap.
Then use an adjustable spanner to remove the valve. Put in the new valve and tighten with adjustable spanner. Replace handle. Screw back in brass screw and the indicator will pop back on.