He will be returning to manage the first team after leaving Workington last summer to take up an assistant head coach position at Falkirk.
Chris Willcock was brought in to replace Grainger, but it was announced on 4 May that Willcock would be leaving the club.
Grainger said: "We want to get out of this league, obviously it's going to be a really tough league this year with Macclesfield coming into it, a full-time team who is budget so we know it's going to be a real challenge as well as probably seven, eight other teams that are going to be pushing for them promotion places."
But this hasn't put him off as he said the team will be "hitting the ground running" when he steps into his new role.
Due to the pandemic, the football league was stopped suddenly when Workington Reds were ten points clear with seven games to go, which Grainger described as "really frustrating".
He said: "The work that the lads had done from sort of June time right the way through to when the season got stopped, it was all for nothing.
"But again when I say that the pandemic was something that over everyone's lives and looking back now you said 'it was crazy times behind us'."
Despite this happening, Grainger thinks it will contribute to him being a better manager now.
He said: "On the football side of it, I've gone away, I've learned, I've got no regrets in what I've done.
"I've gone up there, I've worked closely with a manager I that I got on really well with and I still do and I've learned enough on the pitch now that hopefully I can implement it myself and help Workington be successful this season."