Any invocation to our Lord can be used. Or a simple/double genuflection can be used with the sign of the Cross. Some invocations that are suitable if you wish:
Lord Jesus Christ, Son of God, have mercy on me a sinner.
Most Sacred Heart of Jesus [hidden in the blessed Sacrament], have mercy on me.
May the Heart of Jesus, in the most Blessed Sacrament, be praised, adored and loved with grateful affection, at every moment, in all the the tabernacles of the world, even till the end of time.
Let us forever adore the most blessed Sacrament!
O Sacrament most holy, O Sacrament divine! All praise and all thanksgiving be every moment thine!