Defective silicone joint in the shower area

Our installation situation is very similar to the picture - only everything is still intact.

But what I wondered is, how do you repair such joints yourself and properly? So far, that has never been my problem and I won't find anyone who can make a fair price for doing 2m of joint sealing in the bathroom?

Maybe a janitorial service that has properties nearby. They drive around with those dog catchers, just talk to them. They might do it for twenty bucks. Or just do it yourself, it's not rocket science. Cleaning thoroughly beforehand is the most important thing. Then prepare two cartridges of sanitary silicone, a spray bottle with dish soap water, and plenty of kitchen paper. And then repeat as long as it looks nice. Or until you just can't be bothered anymore.