Forgot to add affidavit in appeal

With permission of court you can file affidavit other wise you will have to amend your appeal by filing amendment petition. 

You can file a petition seeking permission of court to file the affidavit that you ommitted to file along with appeal. 

Generally, a affidavit is not required to support memo of appeal itself however if appeal contains assertion of facts out of record or contradict evidence then it is required in that situation you have to seek permission of court. 

Move an application to file an affidavit to support assertions made therein your appeal.

Are you a counsel or party to the appeal ?

Which type of Appeal? Which Court.

Generally, appeal from the judgment of a civil court could be in the form of Memo of Appeal. No affidvit is required.

Moreover, had the affidavit a mandatory requirement the Court could not have numbered the Appeal.

Even in Revision petition supported by a certified copy of the order of the court attached to the petition, no affidavit in support of such facts is necessary, and the same is with Appeal petition.