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. Then click on Update, and save.
Create a new Text post in the Tumblr dashboard.
Paste this shortcode into the post. If you expand the post, you will see your new POWr Form Builder. Click the POWr Settings Icon to set up POWr Form Builder.
Start to customize the Form Builder Plugin:
Visit your live Tumblr website and click the settings gear in the top right corner of your Form Builder Plugin.