Finding unique k-mer

[yliasolom]

maybe it would be a little silly question, sorry but I am new in bioinformatic. Could you please explain if I have a file with clusters of transposons:

For example: >RLC_02.01.01.05.99_LTR_AVESA_chr13_1474_chr7A_311197774_311206040|RLC_02.01.01.05.99_LTR_AVESA_chr13_1474_chr2A_237772346_237781533|1871
TTATTTTGCATGCTATAATTGTATTAATACGGAAACGTTAATACATGTGTGTTTAATAAACAAACAGAAAGTTCCTAGTTAAGCCTCTCTCATAAACTAGCTCGTTGATTAACAAGATGATCAAGGTTTCCTGATCATGGACATTGGATGTTGTTAATAACGGGATCACAACATTAGTGTAATGATGTGATGAACATTCATCCGAAGTATAGCATTACGATCAAAGTCATTGAGTTTATATTGCTATAACAACTTACGAAGTGATCCTAATCCTTAGACCATGAGATCATGTCAATCACTAACACCGGAAGAGTTTCTTGATAACATCAAACGTCACACCGTAACAGGGTGATTATAAAGATGGATTCAGAACTAATAAAGTGTTATGTTGAGGCTCATGGATCGAGAGTGGAATTTGTTCATCCCGATGACGGATAGATATACTCTGGGCCCTCTCGGTGATATCACATTGATTAGCTTGCAAGCAAGTGATTTGATCACTAGAATGTTATATCACAGGAACGAGAAAAGAGTGCATGTCGGTAACGAGATCAAACTAGGTATGGAGATACCGATGATCGAATCTCGGACATGTAATATATCGTGAAACAAAGGGATTAAGATACTAGCGTAAAAGGTTCCGACGATCACAAGAAAGTCATCGTTGAATGTGTGGGAGTCAGTATGGGTCTCCAGATCCCGCTTCTGATTATTGATCTGAG

How can I implement your tool to find a unique k-mer with length 23 in this sequence?