Here is a sample script to do what you are looking to do.
//Define Variables needed for script
var provider = '';
//check PV1-7.2
if (StringUtils.isNotBlank(qie.doTableLookup(message.getNode('PV1-7.2'), 'notFoundValue', 'tableName', 'column1', 'column2'))) {
provider = qie.doTableLookup(message.getNode('PV1-7.2'), 'notFoundValue', 'tableName', 'column1', 'column2');
// check PV1-8.2
} else if (StringUtils.isNotBlank(qie.doTableLookup(message.getNode('PV1-8.2'), 'notFoundValue', 'tableName', 'column1', 'column2'))) {
provider = qie.doTableLookup(message.getNode('PV1-8.2'), 'notFoundValue', 'tableName', 'column1', 'column2');
//check PV1-9.2
} else if (StringUtils.isNotBlank(qie.doTableLookup(message.getNode('PV1-9.2'), 'notFoundValue', 'tableName', 'column1', 'column2'))) {
provider = qie.doTableLookup(message.getNode('PV1-9.2'), 'notFoundValue', 'tableName', 'column1', 'column2');
}
//If the provider was found update TXA-22
if (StringUtils.isNotBlank(StringUtils.trim('provider'))) {
message.setNode('TXA-22', provider);
}