Belt tensioner no longer tensiones 🙁

hello my friends 😉 the belt tensioner on the driver’s side no longer pulls the belt properly, if I want to strap off and get out. the belt even often hangs in the door when I reach it. otherwise, however, it still works 1a, so safety-wise. ask: can I remove the somehow and clean/oil? or rather buy a used andren, if that bothers me so much.