It's a piece of **** to replace belt. If it were me I would replace both belts.
To remove p/s belt you will need a 40 or 45 torx and 21mm spanner. Hold outer part with spanner and loosen torx. This will slackened tensioner on belt. Remove and refit belt. Tension by turning spanner till belt is tight. Tighten torx.
Be CAREFULL not to remove torx compleately
Slackened studs on alt mounting points. Alt should slide down allowing belt to be put on. If treaded bar showing with nut for 10mm spanner, tighten nut tp tension belt. When tensioned tighten all studs