Allow the strip heater to heat up. You don’t want to try bending the sheet too soon or it will either break or simply not hold its shape.
Insert the sheet between the tubes of the strip heater so that the tubes are at the place where you want to bend the acrylic sheet.
Bend the acrylic into the position you want. Bend away from the heated side because this side will have more give to it and be less likely to crack.
Bend the plastic slowly because even heated, fast movements could snap the plastic. Use clamps and weights to hold the acrylic sheet in the shape you want.
Allow the acrylic to cool while in its new shape. You can allow this to be done on open air with something that will hold the sheet in place until it is fully cooled, or you can place the sheet in a cooling jig if you have one.