Try entering the generic failsafe mode (if your router has a button to press)
https://lede-project.org/docs/user-guide/failsafe_and_factory_reset
Ps. There is no 30/30/30 reset in Openwrt/LEDE. That advice is generally from ancient times with dd-wrt etc. for routers that had "shortable" nvram memory modules (instead of modern flash, where all settings are normal files).
(not quite sure if the router-specific failsafe advice for https://wiki.openwrt.org/toh/linksys/wrt610n#failsafe_mode works for you as the Linksys E3000 is based on the same hardware as the Linksys WRT610N v2.0 with changes to the CFE.
And in LEDE it is ssh always, not telnet)