Number #4 in the diagram below is the gearbox input shaft end cap on a SEAT
Leon Mk2 manual 02Q gearbox. If you have a metal end cap then it will be additionally held in with a circlip (#3). If you have a plastic one it will just be pressed in without a circlip...
To remove a metal one you need remove the circlip, then puncture it with something (i.e. a screwdriver) and hook it out. VAG has a special tool to extract it as shown below but you can just lever it out as long as you are careful not to damage/score the gearbox housing where the cap creates a seal against it...
To remove a platic one you need remove all the lugs being careful not to damage/score the gearbox housing where the cap creates a seal against it, then carefully just lever it out...
To fit either type of end cap, VAG have special tools that is used to press/tap the new cap back in but you can improvise with something as long as you end up pushing it in evenly all round the edge. Just use a piece of wood and a mallet to keep tapping it all around the edges in a circular motion to slowly ease it in. Then for a metal end cap, finally refit the circlip.
For reference, this is the special VAG tool for fitting a metal end cap...
And this is the special VAG tool for fitting a plastic end cap...
