How do i put a rim on a tire? ?

it not really a rim but i have a kia optima and i went to the tire shop and wanted them to put on my spear tire cause i have a doughnut on it and they said that will charge me to put the rim on but last time i went it was free so idk and i have no money so i wanna do it myself and i know i am a girl but i do know how to change a tire just not a rim on a tire please helpp!!!!!