Unable to level up your favourite Heroes because they either keep dying in battle, or you just don’t have enough Shards and Crystals? Not to worry, the new event will take care of that!
The new event is the Helping Hand event and instead of adding a new map, it adds new quests that are easy enough to do, as you only need to KO 5 enemy units, whilst using specific units. (Colorless, Red, Green, Blue, Calvary, Armoured, Infantry and Fliers.)
Furthermore, because the quests solely state defeat enemies and mentions nothing about them being over a certain level, to make things easier on yourself and speed up the process of accomplishing them all, you could always pay a visit to the Training Tower and repeatedly play the very first level (Starting Stratum) as it only costs 1 Stamina and all too easy to beat enemies so earning the full 12,000 Universal Shards will take no time at all and easy to do in a single gaming session.
Or you can do it the hard way to really challenge yourself, the choice is yours.
Source: Fire Emblem Heroes (Mobile app)