Download the file on your PC, connect your Android 5.1.1 device via USB, select "File Transfer" mode, and copy the .apk file to the Downloads folder. Then tap it in your file manager to install.
If you want a browser that is actively maintained for Android 5.1.1, consider these open-source options (search for their APKs on APKMirror): google chrome for android 511 link
If your primary use is banking or sensitive logins, upgrade your hardware. But if you just want to read news, watch cat videos, or use a secondary device, Chrome 90 on Lollipop is still kicking. Download the file on your PC, connect your Android 5