Increase duration of comp with the keyframes

You might be able to get away with selecting the keyframes, right-clicking and selecting Rove Across Time.  This will refactor the inner keyframes to create a smooth curve, but it will also allow you to move the last keyframe and the others will stretch out accordingly.

If there is no video in the composition, the easiest thing to do would be to drop the shot composition into a longer composition, then apply Time Remapping and just extend the layer and move the last keyframe.

You will have to do so manually..however, to move the keyframes proportionately you use the alt key technique to scale the keyframes  proportionately check the following video - https://www.youtube.com/watch?v=PFbFUvfMVgE

Or

You can use the plugin to automate the task i.e. Elastic-comp-changer -  https://aescripts.com/elastic-comp-changer/