How can i refile my 2018 refund

You do not refile your refund.  You cannot refile a tax return that you have already filed. 

You could, if it is appropriate, file an amended tax return.  But, there is a lot more information that you must provide .... Like starting with a detailed question that clearly explains your problem/situation.

Is “re-file” a typo and did you really mean “e-file?”  Or was your return rejected and still needing to be filed?  E-filing is closed forever for 2018 returns. A 2018 return must be printed, signed and mailed.