Last word is "that". Pronoun refering to something specific. Alternatives could be "this", "it", "those". Or maybe "that" is part of the phrase "this", "those", "such". Wait, "that" is a demonstrative pronoun. Replacements might be "this", "it", "those". But need to see the context. In "help with that", "that" refers to the thing being helped. So possible options: those.
Substituting each word:
You should not support on it.
Another check: For "with", the options of "regarding", "on", "concerning" might work in the sentence. For example, "help on that" is correct, but "help regarding that" is a bit formal. Maybe "regarding" is okay.
"I" → You/He/They "can't" → cannot/must not/should not "help" → help/aid/support "with" → regarding/on/concerning "that" → this/it/those