Hi,
For DL ENB will send DCI to intimate which transmission mode ENB gonna send data, there are several DCI formats are available once UE decodes DCI from PDCCH UE will come to know which DCI format it is, then based on the DCI formats UE will decide which transmission mode ENB will send data in PSDCH.
UL DCI formats are DCI0 or DCI 4, these two are the UL DCI formats which will say UL transmission mode to transmit UE data.