How to add snmp to TL-WR740 on 18.06?

[kofec]

You should compile your own image:
About the basics of image compilation - you can find

https://openwrt.org/docs/guide-user/additional-software/beginners-build-guide 4
https://openwrt.org/docs/guide-developer/build-system/install-buildsystem 4
https://openwrt.org/docs/guide-developer/build-system/use-buildsystem 3

Read a little bit about optimization - examples:

Optimized build LEDE 17.01 / OpenWrt 18.06 / libreCMC for "small devices" TP-LINK WR740N(D) WR741N(D) WR743N(D) WR841N/D) All Versions

This is not the right topic to ask for the basics of image compilation. https://openwrt.org/docs/guide-user/additional-software/beginners-build-guide https://openwrt.org/docs/guide-developer/build-system/install-buildsystem https://openwrt.org/docs/guide-developer/build-system/use-buildsystem

OpenWrt 18.06.1 Build for TP-Link TL-WR841N(D) All Versions

It is generated with the make menuconfig command. To customize your own build, remove the # in the make menuconfig near the end of the script. That will open customization menu.

and the maybe you find enough space for snmp