I bricked it mine trying to install a custom OpenWrt image, I was able to get in the U-Boot Web UI pressing and holding the reset button all the time, although I don’t know if it’s the right way.
Righ now I connected via serial port pressing " gl " to stop the booting.

U-Boot 2017.03-armada-17.10.2-gc5a0d2c (Sep 01 2019 - 18:20:09 +0800)

Model: GL.iNet GL-MV1000
       CPU    @ 1000 [MHz]
       L2     @ 80  [MHz]
       TClock @ 200 [MHz]
       DDR    @ 800 [MHz]
DRAM:  1 GiB
U-Boot DT blob at : 000000003f715098
Comphy-0: USB3          5 Gbps
Comphy-1: PEX0          2.5 Gbps
Comphy-2: SATA0         6 Gbps
SATA link 0 timeout.
AHCI 0001.0300 32 slots 1 ports 6 Gbps 0x1 impl SATA mode
flags: ncq led only pmp fbss pio slum part sxs
PCIE-0: Link down
MMC:   sdhci@d8000: 0, sdhci@d0000: q
SF: Detected w25q128fw with page size 256 Bytes, erase size 4 KiB, total 16 MiB
Net:
Warning: neta@30000 (eth0) using random MAC address - 66:40:17:d9:17:6e
eth0: neta@30000 [PRIME]
Hit "gl" key to stop booting in 2 seconds