How do I take over an inactive fanclub?

You can't "take over" a club. Clubs aren't owned sa pamamagitan ng the person who started them - they're owned sa pamamagitan ng every member. However, you can still get the icon and banner changed. The method is different depending on whether the club has 10 or madami members.

The first thing you'd need to do is start a pagtitip. thread in the club asking people to suggest new icons and banners. Leave that running for about a buwan or two. Then,if the club has less than 10 members, you make 2 presinto asking members to vote on their favourite icons and banners, then message one of the F4 asking them to change the club's appearance to the winners. If the club has madami members, you need to use the buttons on the tuktok right of the club's main page which say "suggest a new banner/icon". These make presinto which cost members 5 golds to vote (to discourage uninterested people from spam-voting) and the icon and banner get automatically changed to whichever win these polls.