How do you alter feedback that you left

[plpmr]

Both 61stephenuk and ruby*tuesday are correct.

you have left a positive and a negative with the same comment - both can be remove for feedback policy violations if the sellers report you.

[61stephenuk]

As it's a positive feedback it cannot be revised but you can leave a follow-up feedback if you want to add a correction.

[ruby*tuesday]

By asking the Seller to send You a Feedback Revision Request.