Completely forgotten almost everything past basic maths

So I'm in Year 2 of my T-Level DPDD College course, and I'm planning to study Computer Science in University, and I'm wanting to get my maths skills back up, but I've come to realise that I don't know how to do anything, I was looking at the most basic of concepts that you'd learn starting GCSE maths and I've completely forgotten, and it's quite obviously making me really frustrated.
I can't find any platforms that can give me a good starting point to go off of and every other issue is just one of those kids who go non-stop for 9 hours a day and complain they're not revising enough, I partly blame myself because I pretty much gave up in Year 11 on account of the maths teachers at my school being terrible, I still passed Higher with a 5 though.
It feels like there's a lot of just purely irrelevant stuff added that just isn't needed but if anyone can provide me with some good places to go from it'd be a massive help, and please just don't bs me.