The offer to return a favor should be specific enough to become useful.

Anything I can do is a warm sentence that puts the work back on the other person. They now have to think of a task, judge whether it is too much, and ask you for it, all while being the one who needed help in the first place. The offer is sincere and unusable, which is why so many are never taken up.

Offer one definite thing instead: a Saturday, a lift on Tuesday, the paperwork, dinner on Thursday. Name it and let them decline it, since a specific offer is far easier to accept than an open one.