You bought 2,760 shares @ €3.90 = €10,764
You probably also got 110 free loyalty shares (1 for every 25 held) giving a total holding of 2,870.
For this you would have got 1,358 (2,870/2 x 0.9467) shares in Vodafone and a payment of €3,831 (2,870 @ €1.335) from Valentia.
Your Eircom losses are €797 (€3,831 less 43% of €10,764). You subtract this from your First Active gains.
Capital gains is a self-assessment tax. It's up to you to tell the taxman how much you owe. He's either accept your figures or select you for audit.