You need to glue or tape it back together. You will have to be careful which glue you use so as to not melt the foam. I have used epoxy. I have also used the tape made for seaming vapour barriers in houses. What ever glue you use make sure it is compatible with foam. Your hobbyshop should be able to guide you.

The other issue you will have to deal with is to make sure to re-balance the model after adding the extra weght on the one side.

I have had several electrics. After only a few flights they all ended up in the garbage.

Best of luck!!