After Toolkit > Modifiers > Extend
Maximize layers' duration in After Effects
Extend the duration of your layers to fit your composition's or your work area's length.Extend adapts your selected layers' duration to fit your composition's duration or your work area's duration.
Extend - Quickstart Guide
Open your After Toolkit, select your layers, and click on Extend.If any of your selected layers is footage or a precomp, you can make it loop while extending it.
You then have two duration options for your selected layers' new length: Composition or Work Area.
If you don't have any layer selected, it will extend every layer in the active composition.
