I assume you most likely used metafor for this and its included rma.mv function.

You can add fixed covariates using the mods argument to rma.mv - this is completely separate to the multi-level error structure. For example, using one of the example datasets built into metafor:

library(metafor)

##multilevel model without covariates

model1

Use an explanatory variable that will define the level

Jack Henry thank you so much for your help, i think that it can result with our data.