It is not possible to change a TFSA account to a margin account. If you want a margin account then you must initiate a new account application for a margin account.
Additional Information
How to change my TFSA Account to a Margin Account
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How do I add an account?
How do I change my account type if I selected the wrong one?
Can I deposit funds as the second owner of an IBKR Joint account?
Can I convert my individual account to a TFSA account?