Sure you didn't just disable them if it's not rooted? What were the pre-installed apps? If you can find them on Google Play, e.g. Facebook, that's not a problem, just re-install them. If it was apps specific to Lenovo and this phone, might have to contact Lenovo about that. May even involved re-flashing the manufacturer's firmware to restore them. Have a look in Lenovo's app store see if anything is there, as long as it wasn't the Lenovo store itself you removed. Some pre-installed stuff (bloat) can sometimes be removed without rooting, others requires root.