Edit Appearance Edit Theme
In your Tumblr dashboard, open your Account Settings. Select Edit Appearance and click Edit Theme.
Go to Edit HTML.
Paste the Script
Paste this script into the Tumblr HTML file. It's always best to paste it between the Head tags. Update, then save.
Create a new Text post in the Tumblr dashboard.
Paste this shortcode into the post. Expand the post to see your new Membership Form plugin. Click the Settings Icon to launch the POWr Editor.
Start to customize the Membership Form Plugin:
Visit your live Tumblr website and click the settings gear in the upper right corner of the Membership Form Plugin.