How to enable text chat/text box in CSGO?
I suppose you used hud_saytext_time 0 to hide your chat. In this case anything higher than 0 will "unhide" it. The number represents the time in seconds the chat will stay visible before it fades away. So a value of 0 displays the chat for 0 seconds, 10 for 10s, etc.
So in your case you can use hud_saytext_time 12 to display the chat again and after 12 seconds the messages fade away again. 12 seconds is the default value, but you can use any other number as well.