Once you have collected a sufficient amount of shield restoring and healing items you need to bring them up by either pressing the 'Up' button on the d-pad of the PlayStation 4 or Xbox One controller or if you are playing on PC by pressing '4'. Find a safe place before you start the process. The regeneration process of these statuses takes a few seconds, if during that time another button is pressed the countdown will reset. Your character can however move which it is advised to do as a moving target is more difficult to take down than a stationary one.
If you have the Lifeline
character in your squad the player controlling her will be able to heal you with her Tactical Ability by the pressing LB button on the d-pad of the Xbox One or the L1 button on the d-pad of the PlayStation 4 , or if you are playing on PC by ressing 'Q' . This will place a small drone that hovers about a foot off the ground and heals nearby allies within the limited range. A small tube will extend to the ally to indicate that they are being healed.