When one tax year ends (5th April), and a new one begins (6th April), the tax-free allowance in your Trading 212 ISA is automatically reset to £20,000. You'll not need to open a new Trading 212 ISA, as you can accept the ISA declaration and add funds for the new financial year directly in your existing ISA with us.
No further deposits should be made to your Trading 212 ISA if you decide not to contribute in the new tax year. Holdings from previous tax years can be kept and reinvested.