Problem installing istioctl via istioctl

Use the guidance of the official istio community,
After I downloaded the istioctl version 1.8.0, I used the istioctl command as follows:

istioctl manifest apply --set

Error: unknown flag: --set
How to use --set

istioctl manifest apply isnt a valid command. maybe try istioctl install

:arrow_forward: ./istioctl manifest
The manifest command generates and diffs Istio manifests.

istioctl manifest [command]

Available Commands:
diff Compare manifests and generate diff
generate Generates an Istio install manifest
install Applies an Istio manifest, installing or reconfiguring Istio on a cluster.