The L850-GL is based on an Intel XMM 7560 modem chipset. This chipset has known AT command backdoors that allow IMEI reprogramming if you can enter low-level diagnostic modes. However, modern firmware (post-2019) from Lenovo, Dell, and HP has patched many of these vulnerabilities.
Tools like or Wwr_IMEI_Writer are often required. Disable antivirus – these tools are frequently flagged due to their unsigned nature (use a sandboxed environment). fibocom l850gl change imei work