This is one possibility. Can't tell for certain without make and model:
1. Tap. Unscrew the domed chrome ring near the front. Then unscrew the plain chrome ring behind it. The square chromed plate is probably stuck to the wall with silicone. Use a large sharp knife to cut through the silicone and remove the plate. This is assuming you need to access the pipe connections. If the valve only is leaking, you should be able to get it out after removing the domed chrome ring. It may require a special spanner.
2. Spout. Unscrew the spout from its wall plate. Again the wall plate is likely to be siliconed in place. Cut through the silicone to remove the plate. When you come to reassemble the spout the trick will be getting it to point in the right direction. Probably the easiest way is by using Loctite 55 thread cord as a sealant. You can unwind the spout up to 1/3 turn to get it to point in the right direction. PTFE tap is less forgiving. Liquid PTFE is a possibliity but requires both parts to be scrupulously clean, and in particular, grease free.
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