how to enter an ira to roth conversion, if my 5498 is not available

Enter the Form 1099-R that you should have received which is reporting the distribution from your Traditional IRA.  Then answer the follow-up questions to indicate that the funds were converted to a Roth IRA.  That will report it as a conversion.

Be sure that you include any information about the basis of the Traditional IRA account so that the taxable portion of the conversion can be calculated.  

It is not necessary to have your Form 5498 as long as you have a statement showing the account value at the end of December 2024 for all Traditional IRA accounts that you have.