The last two bars of a Blues progression is called a "turnaround". A turnaround is a short series of chords that will take you from I back to V leading back to I again. The turnaround in basic form in the key of Bb is:
A Jazz player would more commonly play:
Many other variations are possible, e.g., in the basic Blues which follows try substituting the different turnarounds given in place of the last 2 bars. You will notice that they all lead back to the I chord.