First, select a dynamic picture, press and save it to your mobile phone.

Then open any dialog box and click the+sign to add an expression.

After entering the next page, click the Settings button in the upper right corner.

Select "My favorite expression" from the drop-down list.

Select the "+"sign at the bottom to add the dynamic pictures saved in the mobile phone.

Finally, when chatting in the dialog box, click the red heart to see the dynamic picture just added.