How can I set bootargs on the buildroot(setenv error)?

Question

I want to set the bootargs on the buildroot system.

I have set the command line like the following.

setenv bootargs rootfstype=ubifs rw ubi.mtd=10 root=ubi0_0 console=ttyMH0,1152
00n8

But the following error message was diplayed.

-sh: setenv: not found

How can I set the bootargs?

My system environment is like the followings.

# cat /etc/*release
NAME=Buildroot
VERSION=-g81c40b5
ID=buildroot
VERSION_ID=2020.08.2
PRETTY_NAME="Buildroot 2020.08.2"

Thanks.