"Re: Change that the individual can be claimed by someone else, I tried to override but could not do it."

Did you Efile it and it got rejected?  What are you trying to override?

If the child is being claimed by the other parent, but your client still qualifies for HOH since the child lives with them, then you need to mark it with Code Q in the dependent entry section.  If the child is being claimed by someone else and your client cannot claim them at all, then you need to delete the dependent (right click on the dependent line and choose Delete Line)