[Help Wordpress] Specify image dimensions

Specify image dimensions

Hi!
I have a question, how can I specify image dimensions in this code?
because gtmetrix says that the images and thumbnails (thumbnails in the bottom of the imagenes) I dont specify dimensions
I dont know why because in Image Options I seted it up
Main image width: 428
Main image height: 518
Thumb image width: 96
Thumb image height: 72

what should I do?

  {{image_tag}}
  {{thumbnail}}
  {{html}}
  {{animated_blocks}}
  {{title}}

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