Log in to your account with Namecheap and click on Account at the top right of the screen if your domain name isn’t already listed on screen.
Click on the Manage button to the right of the domain you hope to redirect. \ \
Click the Advanced DNS button on the top right tab.
Look for the Host Records which may be any combination of A Record, CName Record, Alias Record, URL Redirect Record, etc.
I hesitate to tell you to delete any but you need to set an Alias Record with the host being an @ symbol, the Value is your Netlify address for your app (in my case nostalgic-torvalds-afe855.netlify.com [it seems to add the trailing period after I save it]) and TTL to Automatic. To make sure any request going to your domain name including www you need a second record, a URL Redirection Record with a host of www, your domain name (in my case http://lindadove.net [without the www]) and Unmasked selected.
You may have to wait up to 20 minutes for the changes to take effect and remember to do a hard refresh (Command-Shift-R on a Mac) or check the site in a Private/ Incognito window so you aren’t getting a cached old version. Let me know if this doesn’t work for you or if you have improvements. Your next best bet is to go directly to Namecheap’s support chat.