Custom genomic regions should be provided in BED format and can be given by admire -r regions1.bed -r regions2.bed ....
Hint: Use multiple -r parameters to analyse more than one region at a time.
Hint: The BED format is described here
To enable the Gene Set Enrichment Analysis for a certain bed file, include a gene_name property in column 4 of the bed file:
chr1 213941196 213942363 gene_name=gene1
chr1 213942363 213943530 gene_name=gene2
chr1 213943530 213944697 gene_name=gene3