What does it mean when asks if u want to use ur last year's earned income?

[Critter-3]

It means you have the OPTION to use the prior year earned income to get a bigger refund ... READ the screen carefully to decide if this is something you want to do ... if you don't get a bigger refund you can undo your choice.  It is an OPTION not a REQUIREMENT  but since returns that have EIC in them will not start processing until mid to late February  you have the time to make this decision.

[Opus 17]

If you lost income this year due to the coronavirus, that might also cause your EIC to be lower.  One of the coronavirus relief programs is the ability to choose to receive your EIC in 2020 based on your 2019 income if it gives you a higher payment then your 2020 income. You are allowed to calculate it both ways and choose which ever is best for you. The other answer shows examples of how this works.

[Critter-3]

Interesting that the program only asks for the 2019 earned income amount and not also the AGI  since the EIC is computed using both amounts.  This is a weird situation that I don't think was thought out well and I don't see how the program can extrapolate the info if it was transferred from the prior year ... I don't see it happening in any of my test returns at least not yet.   And the help info is poorly done ... they should make it simpler by citing form/line numbers.  And is the IRS ever going to catch any taxpayer data  errors ?   Will they recompute the return for the taxpayer if they cheated themselves ?   This is so unprecedented and  the IRS is already stretched thin.  What a mess.