restarting migration from my 2008 imac to my 2017

i had to quit migration from my 2008 (el capitan v10.11.6, 20 inch) imac to my 2017 (high sierra v10.13.1, retina 4k 21.5 inch) imac. when i restarted the process, 2 (duplicate) conflicts needed resolution. i wanted to select the "replace" and continue operation, but the default is set at "keep both". how can i utilize the "replace" option, as i do not wish to have duplicated files from the first attempted migration.