You can manually compress images in two ways:
1. Open the Crush.pics app and click Batch Process in the top menu
2. Click Compress # Images
1. Open the Crush.pics app and click Details next to the image you want to compress
2. Choose Conservative(Lossless) or Balanced(Lossy) Compression and then click Compress
Note: There is no way to stop or cancel a batch process action. You will need to wait for it to finish and then you can undo the action by compressing or restoring the images.