My T101 contains an amount in box128. If I enter the same amount in the ITC form it seems to double count the total ITC, where should I enter the number?

Alternatively, if I enter the amount on my T101 and then leave the amount blank in the ITC form, it will allow me to carryback the unused (correct balance) which I would like to do (also posted related Q on this as it doesnt seem to change the tax balance).  So maybe that's what I am to do?