You must keyframe the linear wipe effect.
I would highly suggest starting your AE life with the resources on linked here. AE is not a program you can just fiddle in and pick up. You have to have a good foundation. Luckily there are tons of great free(!) resources in that link I provided that are specifically aimed at helping people like you get started in AE.
– The Great Szalam
(The ‘Great’ stands for ‘Not So Great, in fact, Extremely Humble’)
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