How do I increase the postage AFTER a sale

[sm-349492]

I am quite prepared to add an amount tas the package is bigger than expected... how can I do this to an existing sale with a tracking number generated?

[plpmr]

once sold you cannot charge extra.

[sm-349492]

Hi, I am prepared to cover any extra costs but do I need a different
postage label and therefore a different tracking number OR can I just pay
extra. Thanks.