I don't think that's the correct tool - that's used on the old style VW to press and insert the circlip.
For the Sharan/Galaxy Zetec 2003 TDI 6 speed - both have to same setup. You need something to press the outer housing and hold it down, then insert a threaded bolt in the middle and tighten.
I'm trying to use a bearing press and press against the anti-roll bar - will try it tommorrow.
Sorry I saw the mk2 in your OP so I was assuming you had the older 020 trans
The 03 should be the 02J box. These can be quite hard to press in, and as far as I know, VW does not make a tool for this step.
If the trans is still in the car, you should be able to use the K frame as a leverage point to press in the drive flange while tightening down the bolt.
If it’s out of the car, your going to be creative. I’ve used my 30 ton press to gently press it in
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