The best way to use OceanHero as your regular search engine, is to create an icon for it on your home screen. It is very simple:
Step 1: Go to oceanhero.today/search
Step 2: Click on the share icon
Step 3: Click on "Add to Home Screen"
Unfortunately, it is not possible to change your default search engine in Safari due to Apple's limitations. But adding OceanHero to your home screen on iOS makes it easy to use.