How to get higher rank in Gtmetrix for image issues?

Hello i am Arijit and i run a website Rapid Weight Loss Care.

On which i am currently having some issues regarding site load being too slow.

So i used gtmetrix to see what problem i have and found that majority of the issues are related to image.

On page speed test (Google) i get a very low score on mobile as well as desktop version.

Any suggestion on how i will optimize that issue asap…

I tried all possible plugins but non helped.
I also referred to different posts on that issue on this forum but non helped.

When i click those links on gtmetrix i see a suggested dimension. But i find all my posts automatically applies image dimensions via small, medium, or large tags on media settings of wp dashboard.

So my question is how will i set specific image dimensions to images that are in featured image or thumbnails.

And most importantly i don’t know coding so what ever your suggestions will be please be brief…. ??