How do you replace an alternator on a Citroen?
Hook up with an auto parts store to get a replacement. If the unit is an “oddball” and you can’t find one relatively easily, call around and find a shop that rebuilds them. There may be one closer than you think. Get your new or rebuilt unit and use the reverse process to install it. You’ll have to get a “pry bar” or something to put some tension on the belt before you tighten the last fastener to lock the alternator in place to hold that correct tension. Put your wires back on the way they came off, and hook your battery back up. Work safely at all times. Good luck.