Do Imperial accept resits

HelloI am hoping to apply to Imperial college London. I got an A (below 90) for AS math and want to reset in order to get an A* for a level.So I want to know if Imperial college London accept reset?

I'm confused with this one. The maximum grade for AS is A, there is no A*. A* is available on A2, a second year of the A-level. If you got A for AS, what do you want to resit ?

I believe that A level are made up of 50% of your AS grade and 50% for your A2 (second year of level studies) grade, so if I want to achieve an overall A* grade for my A-level, I might need to resit.

It's not like that. A-levels are the exams you take at the end of year 2 and those exam results = your A-level grade. Many schools don't even sit AS levels, preferring to conduct internal examinations (like mine did).
Now, however, with exams cancelled it's different, and every school has its own rules. Mine, for example, was predicting grades based on no data and no logic, so many people ended up with grades they'd have never achieved otherwise.
Point is, the OP noted that his AS grade was A, which is maximum possible. There is no better result he can possibly achieve, since percentage is irrelevant. Hence, I'm confused with why he would want to resit it.

P/s even if A-levels were calculated in the way you suggest, still, he got maximum possible grade on AS and still wants a resit. It's like resitting an IB subject where you got a 7.

International A levels and A levels in Wales and Northern Ireland are still composed of AS and A2 modules for an overall grade.