You must have valid license to access this content.
You must have valid license to access this content.
You must have valid license to access this content.
You must have valid license to access this content.
You must have valid license to access this content.
You must have valid license to access this content.
You must have valid license to access this content.
You must have valid license to access this content.
I did it for you.
Step1: Set the button link to # or javascript:void(0); or leave it emtpy.
Step2: Add Class ID for the button https://www.dropbox.com/s/omv8k51lu4itehz/Screenshot%202017-05-31%2013.27.43.png?dl=0
Step3: select the popup for this page https://www.dropbox.com/s/7x1j9q8h0eqotyn/Screenshot%202017-05-31%2013.20.31.png?dl=0
Step4: Edit the popup, add the button ID to Tigger Object field. https://www.dropbox.com/s/6bd7ipmm5271you/Screenshot%202017-05-31%2013.26.38.png?dl=0
By the way, you can enable king composer for the popup.