the insert points on virtually all inexpensive mixers are unbalanced. you use a Y cable that has a quarter inch" TRS plug on one end that splits out to two quarter inch TS plugs on the other.
If you want to keep your signal chain balanced, you will have to run your box in series, using the direct out on the mixer channel (or a subgroup output) into the input on your box, then the output of the box to the tape/DAW track input.
BUT... if it is an EFFECTS box (and not a processer) it is more usual to use the aux sends and either an aux return or a spare mixer channel (or pair of channels) for the return.