Susan

I currently a have flexible instant access isa but for 25/26 tax year I am looking to open an instant access isa (not flexible) with monthly income using my full £20k allowance. I don't want to touch the new isa if possible (ie leaving £20k allowance alone). I know I can still withdraw from the existing flexible ISA at any time but want to know can I still replace those funds back into the flexible ISA as at present or will using my allowance in a non flexible isa next tax year stop me from doing this? Thanks