If you know a formula but do not know when to use it, the missing skill is method selection. Memorising the formula again will not solve that. You need to recognise the structure of the problem, the quantities involved, and the conditions that make one method appropriate instead of another.
Practise with mixed questions where several formulas are possible. Before calculating, state what kind of problem you think it is, what evidence in the question supports that choice, and why another method would not fit. This trains the decision that comes before execution.
Use the Mathematics Learning Hub for topic-specific routes, and the Study & Learning Methods Hub for interleaving and method-choice practice.