When can I file a 1040x for 2020?

[03jasonk]

I accidentally entered my W-2 twice.

[pk]

@03jasonk ,  a rule of thumb is to wait till the IRS has finished processing the filed / accepted return ( as signified  on their website or  better still the receipt of the refund).  That is my suggestion

[Mike9241]

I agree with PK since this is something the IRS is likely to catch and automatically change. if you would owe after the change you have until 5/17/2021 to pay.