I hope you are a good Sherlock!
Find a good flat surface as you need it to reference (a single slab of stone or glass top table). Make sure your feet are all present and are uniform (no off the wall solutions)
With the system sitting are the feet all setting firmly on the table surface? Does it wobble? With the lid open you might be able to straighten a slight bend (more than a 1/16th of an inch will require a taking the bottom cover off)
Now you’ll need to take the bottom cover off and locate the screws which hold the screen. Follow this guide MacBook Pro 15" Retina Display Late 2013 Display Assembly Replacement After doing the first four steps, jump down to Steps 9 & 10, then jump to Step 12 just loosening the six screws, then tighten them up again did that fix things? If it did button it up and check again.