Modify list form and make fields read only

Hi Experts,
I am trying to modify SharePoint 365 edit form. I added condition in PowerApps, It works if I am editing it from List but from SharePoint WebPart page it didn't work properly. Is there a way to change this in Modal dialogue box? Like in below image

I would like to make first 4 Fields read-only

- If I select any other value from Dropdownlist other than Unallocated then Next dropdown list should be disabled.

How can I achieve that any idea? I am not using any custom code or designer as I have limitations to use both. I want this to be OOTB. 

Please guide.

Regards,

Abhijeet