Can't enter 0% for T5 percentage.

Joint account with my wife but she contributes 100%. T5 issued with my SIN so entered it on my return. Cannot enter 0% as "your percentage" as it defaults back to 100%. How do I enter 0% as my percentage?

Self-employed

It will need to be entered under your wife's name since as you said she contributed 100% you can't claim 0% when you enter a T5 in your name. So you will need to  enter it under her name.