The Blues comfortably made it through to the next round of the EFL Cup, with a 7-1 victory, but Lampard was not happy with the performance at half-time.
Particularly as one specific plan they had for the game was not being carried out by his players.
“In the first half. With Callum and Christian Pulisic as wingers, the message was to hurt the Grimsby line and run in behind and end up in areas inside the box where you are taking people on,” Lampard told the official Chelsea website.
“It wasn’t happening and at half-time the message had to be reinforced pretty strongly.
“In the second half we managed to get in better positions.
“Callum’s talent means he has to work hard to run behind people, to get at people and be inside and outside and work off the ball.
“That is where he needs to learn, because if he wants to be in the team week in week out that is what he will have to do.”
Chelsea ran out 7-1 winners against Grimsby on Wednesday night, but Lampard has said he was unhappy with the defending in particular at times.
“At half-time I was not very happy with the game. To concede the goal that made it 2-1 was a disaster because I showed them it was a huge threat, the long ball and the second ball in behind, and conceding that made us a bit nervous.
“So it is good for the young players in particular to see that small details, if you don’t watch the video we show before the game and realise the danger, can cost you.
“It was fine tonight because we won 7-1 but against Liverpool we lost the game because of small details.”
Chelsea face Man Utd in the last 16 of the EFL cup after The Reds edged out League One Rochdale on penalties.