change clip duration in premiere Rush

Yes this is so obvious and why i never use Premier Rush

In Premiere Rush, you can only select one clip and change the duration at a time (Here's a link to where you can upvote the feature request on UserVoice).

But, you can still accomplish what you want by opening your project in Premiere Pro. Open Premiere Pro and below the Open Project... button, click on Open Premiere Rush Project... and select your project. With the Timeline panel selected, go to Edit > Select All (or press Ctrl or Command + A) to select all the clips on the Timeline. Go to Clip > Speed/Duration and change the Duration to how long you want each clip and click OK. All of the clips will be updated. Use File > Export > Media to export your video (after selecting your export settings in the dialog that appears).