Help needed Huawei B315s stuck on 4g only

I have bought a Huawei B315s router from a lady that used it with her Spark plan.

I live in a rural area and need the 3G network to work.

For some reason though, the modem is stuck on 4G only and I don't know how to change that. The other options that usually appear with this modem (2G, 3G ecc) aren't there.

How do I fix this? I am assuming Spark has done something to the modem to lock it on 4G only?

Can I remove that woth an update or something?

Thanks a lot!!