The preterite tense is in other words the past tense. Down below I will list the conjugations to saber in the preterite form.
yo- supe (I knew)
tú- supiste (you knew)
él/ella/usted.- supo (he/she/you(formal) knew)
nosotros- supimos (We knew)
ellos/ellas/ustedes.- supieron (they knew)
saber- to know
Hope this helps! :3