<link rel="canonical" href="new page URL" />
<meta http-equiv="refresh" content="0;URL=new page URL">https://dev.to/steveblue/setup-a-redirect-on-github-pages-1o...
Also, these redirects won't help with your Google results until next time they crawl the site, so you may have to wait a few days.
Did you use a custom domain for old version?
I'm still not 100% clear on how the previous domain was configured with github pages
if it's 1) then you should be able to set up redirects for the domain using something like cloudflare to serve the 301s to the old domain.
if it's 2) then there really aren't any more "simple" solutions that you can implement purely technically. You've already added the canonical reference and the meta refresh. You could also add an A tag link to "Download the software on our new website" in addition to the other measures. Users are already sent over via the meta refresh, but the link will encourage crawlers who skip that tag to find you as well.
If your goal is to show up when people search the name of the software (example: "iterm2"), then the solution is to register on every possible social media website you can find and link them to your new domain. In addition to that it's worth using an online PR service to distribute a press release with a link to your new site announcing the new domain.
If there's a more generic term (example: "mac terminal software") then you've got a longer road ahead of you with a regular SEO campaign.
Most of my previous traffic was from direct searches for the name of the software, so I think I'll try the social media approach - thanks!