You need to read the tax rules on buying and selling shares within 4 weeks, as generally can only be used to set off against gains on same class of shares,
And then if multiple purchases you use FIFO basis,
Can you request the holding is transferred rather than sold, bit if you do sell to crystalise the liss you need to wait 4 weeks to ensure you can use the loss on other gains. Likewise when was each holding acquired as assumption is the ones you sell first relate to those you purchàsed first based on FIFO basis, irrespective or where they are held.
Thats my reading of the rules, and i looked at this trying to crystalise loss on paper AIB shares by buying some on DeGiro waiting a few months, sell the electronic ones, and claim loss based on FIFO for when portfolio was acquired, as found it hard to get someone to sell a snall number less than 10) AIB shares tbat have a unrealised loss of over 30k, but vale €25 so less than costs to sell so no one interested in ot even when I would pay the €50 fee to actually sell them.