Brother GTX600NB Instruction Manual page 148

(3) Remove the platen moving it straight upwards by holding both ends of it.
(4) Put another platen to be used in position directly from above.
(5) Tighten the platen fixing handle.
<TIPS>

Place the platen fixing handle sideways so that the platen fixing handle will not come in contact when setting the platen or
T-shirt.
If the platen fixing handle is in portrait orientation, pull the platen fixing handle sideways and turn it in landscape orientation.
Platen
5-15
Basic printing procedures
Platen
Platen
Platen fixing handle