You'll need a third party uninstaller that is much more powerful than windows. I'd suggest using the Free version of Revo Installer. This will delete all the leftover Support Assist registry. Please watch video in link below for additional information that might be helpful to you:

Fix Dell SupportAssist Not Working, SupportAssist Hardware Scan Not Working - YouTube

Also, 

Download Revo Uninstaller Free - Remove unwanted programs easily

I tried Revo and reinstalled support assist still the same problem persists

I am sorry to know Revo Installer did not resolve Support Assist problem.

If Dell Update and Dell Support Assist OS Recovery applications are installed on the computer, I suggest uninstalling both of them, and then uninstall Support Assist application again.

Reinstall all three, hopefully Support Assist works normally now. You can reinstall Dell Update and Dell Support Assist OS Recovery applications from the link below:

Support for Dell G5 15 5590 | Drivers & Downloads | Dell US

If the above steps don't fix the Support Assist problem, I suggest reinstalling windows 10.

For further assistance, post same question in Dell Support Assist Community forum in link below:

SupportAssist for PCs - Dell Community

Also, 

John

Glad to know you have posted your question in Dell Support Assist Community forum.

Thanks for the update.