The assembly guide will be included for you in the box.
However, if you are having trouble finding it, you can also download both the assembly guide and the user guide on the SIDIZ website.
Here are direct links for you :)
T80 : https://www.sidizusa.com/t80
T50 : https://www.sidizusa.com/t50
T50 Air : https://www.sidizusa.com/t50air
T40 : https://www.us.sidiz.com/t40
T25 : https:/t25/www.us.sidiz.com/
Ringo : https://www.sidizusa.com/ringo