To Install DiffBind, you can follow the instruction found at DiffBind

First thing first, you would need to install BiocManager and then install DiffBand

if (!requireNamespace("BiocManager", quietly = TRUE))
    install.packages("BiocManager")

BiocManager::install("DiffBind")

At the end, you should get

To view Documentation,

browseVignettes("DiffBind")